The present invention relates generally to metal containers that can be used in both microwave and conventional ovens. The invention, in addition, is directed to a construction and system that permit the use of metal containers in microwave ovens; the uses are arc-free and non-reflecting of electromagnetic energy.
It has been the general belief that metal containers should not be used to heat and cook food in microwave ovens. Bare metal containers can reflect the electromagnetic energy toward the magnetron (that supplies the energy to the oven cavity) and thereby damage the same. In addition, when bare metal is disposed in close proximity to the metal walls of a microwave oven, arcing between the container and oven walls occurs. For these reasons, the industry has generally advocated the use of plastic or cardboard containers to heat loads, e.g. foods, in microwave ovens.
However, certain exceptions to this prohibition have occurred where it has been desired, for example, to shield one food portion from another in a container to effect differential heating and cooking. This has been effected by the use of metal containers having deep and shallow portions and/or metal strips, often in combination with ferrite materials. Ferrite materials absorb the microwave energy and thereby heat the metal such that cooking or heating of the food is effected at least in part by the use of direct convection heating. There is a large number of U.S. patents which disclose such use of ferrite materials. To list the patents here would be unduly cumbersome and somewhat unnecessary since the present disclosure is not concerned with the use of ferrite materials.